Steam turbines are used in power plants for generating energy. Once commissioned, the steam turbines are operated more or less constantly. However, it is necessary now and again to carry out overhauls. This requires that the steam turbines be taken off-line and cooled. For cooling, it is routine practice to cool the steam turbine using so-called “forced cooling”. In essence, “forced cooling” comprises three phases, wherein in the first phase the steam temperature is reduced during power operation and after switch-off, then natural cooling and finally “cold drawing” with ambient air, the air being drawn through the steam turbine by means of an evacuation device. Thus, the steam turbine undergoes preliminary cooling by means of a reduction in the steam temperature during power operation. This reduction in the steam temperature can be brought about by means of a boiler blow-off and/or by reducing the power of the firing or of the gas turbine (in the case of a combined cycle plant). However, it is necessary to attend that the reduction in steam temperatures takes place so as not to exceed the design limits of the steam turbine. To that end, the steam temperature can be reduced with fixed gradients. However, this has the drawback that any freedoms are not fully exhausted. In turn, this leads to a loss of time, in which valuable fuel could be squandered.